A U-TDOA location system (and other location systems) location performance is normally expressed as one or more circular error probabilities. The United States Federal Communications Commission (FCC) as part of the Enhanced 9-1-1 Phase II mandate requires that network-based systems, such as U-TDOA, be deployed to yield a precision that generates a one-hundred meter (100 m or 328.1 feet) accuracy for 67% of emergency services callers and a three-hundred meter (300 m or 984.25 feet) accuracy for 95% of emergency services callers.
First commercially deployed in 1998, overlay network-based wireless location systems have been widely deployed in support of location-based services including emergency services location. As mobile usage increases, the need for high accuracy and high yield wireless location increases for both commercial location-based services and wireline parity for Enhanced 9-1-1.
An example of the need for a high accuracy, high yield wireless location system can be found in the Federal Communications Commission's 07-166 Report and Order released on Nov. 20, 2007. The 07-166 Order established an original deadline of Sep. 11, 2010, by which time all wireless carriers must demonstrate full E911 location accuracy compliance within at least 75% of the Public Safety Answering Points (PSAPs) they serve; and demonstrate compliance within 50% of location accuracy requirements in all of their PSAP service areas. The Order originally required carriers to achieve full compliance in all PSAPs they serve by Sep. 11, 2012.
To ensure that wireless carriers are making progress toward full PSAP-level compliance, the FCC has instituted a series of interim benchmarks requiring carriers to achieve location accuracy compliance within each Economic Area they serve by Sep. 11, 2008 and within progressively smaller geographic areas (including Metropolitan Statistical Areas and Rural Service Areas by Sep. 11, 2010) until they demonstrate full PSAP-level compliance in 2012. Wireless carriers must submit biennial progress reports (by Sep. 11, 2009 and 2011, respectively) to the FCC describing their progress toward achieving full PSAP-level compliance. Compliance was expected to be based on testing as detailed in the FCC Office of Engineering and Technology (OET) Bulletin No. 71 guidelines; however, the FCC declared in the 07-116 Report and Order that the FCC may define additional testing reporting requirements in the future.
The FCC 07-166 Report and Order has been stayed by the U.S. Court of Appeals for the District of Columbia Circuit and the timelines and deadlines proposed are in jeopardy, but the FCC was clear in its intent to enforce stricter requirements on wireless carriers' E911 systems.
The Commission's stated goal in enacting the new standards that was to allow public safety workers to better locate individuals who have called for emergency assistance from a wireless phone has not changed.
As the FCC moves towards a PSAP-level location accuracy (and yield) mandate, methods for combining different location technologies becomes a necessity. This invention is in the fields of communications and location technology. It provides a means for combining complementary technologies of GPS and UTDOA to achieve accuracy improvements.
GNSS receivers (examples of GNSS systems include the United State's NAVSTAR Global Positioning System and the Russian Federation's GLONASS system. Other examples of GNSS systems include the European Union's proposed Galileo system and the Chinese proposed Beidou Satellite Navigation and Positioning System) generally produce highly accurate pseudorange measurements but in urban environments satellite coverage can become severely limited. In urban environments, UTDOA has the advantage of having better coverage and more measurements but generally provides less accurate individual TDOA measurements. When there is sparse coverage for both systems, neither system may independently be capable of providing a location solution; however, when used together accurate location estimation becomes feasible.
A method and system is provided that efficiently utilizes measurements from both GPS and UTDOA networks to find the position of the mobile station (MS). The downlink pseudorange measurements in GPS are transformed into U-TDOAs and combined with other measurements. Satellites are treated as transmitting towers with very high antenna heights based on the satellite position at the time of the pseudorange measurement.
The inventive techniques and concepts described herein apply all Global Navigation Satellite Systems and to time and frequency division multiplexed (TDMA/FDMA) radio communications systems including the widely used IS-136 (TDMA), GSM, OFDM, and SC-FDMA wireless systems, as well as code-division radio communications systems such as CDMA (IS-95, IS-2000) and Universal Mobile Telecommunications System (UTMS), the latter of which is also known as W-CDMA. The Global System for Mobile Communications (GSM) model and the United States NAVSTAR Global Positioning System (GPS) discussed below are an exemplary but not exclusive environment in which the present invention may be used.